Black Hole is formed by a Explosion of Giant Stars.
If a Star is alive, the inward force of gravity is balanced by the outward force created by radiation and gases. Both inward and outward forces maintain balance and holds the star together.
At some time, the star will run out of his fuel. So there is no hot gases and radiation. Hence, there is no outward force in star to balance the inward force of gravity. So, the star begins to die. The whole star's core is begin to collapse under its own gravity. This collapse causes a huge explosion called a supernova.
If a star has atleast twenty five times more mass than our sun, then the star collapses to form a black hole. The outer layer of black hole surface is called as event horizon. Nothing can escape from within the event horizon of a black hole, not even light. This is a simple definition of Black hole for your understandings. We all know that the first image of black hole is successfully captured by 'EHT' . Dr.Katie bouman, she is the computer scientist behind the first ever image of black hole. She developed the algorithm that turned telescopic data into the historic photo we see today.